Oil-in-water emulsions are used in the hot rolling of non-ferrous metals, such as aluminum, to provide lubrication and cooling. In order to lubricate the contact between the steel roll and the aluminum strip, i.e., the roll bite, the emulsion needs to be able to form a protective film on the roll to reduce friction and to prevent metal-to-metal contact. Rolling is performed in the mixed lubrication regime. In this regime, the lubricant needs a certain viscosity to form lubricant pockets, as well as a chemistry to provide strong boundary films. It is in the boundary film that the lubricant forms a bond with the rolling surfaces.
Because of the high pressures in aluminum hot rolling, any hydrodynamic lubrication is elastohydrodynamic (EHD) lubrication. In this type of lubrication, the high pressure prior to the actual point of contact causes the viscosity of the lubricant to increase significantly. Under such conditions, the film thickness is determined by the viscosity and also the pressure viscosity coefficient, which indicates how rapidly viscosity rises with pressure.
A problem in the traditional rolling of oil formulations is the formation of metal soaps. These soaps form from the reaction of aluminum with the fatty acid included in the formulation as a boundary lubricant additive. These soaps are highly viscous and cause an increase in oil phase viscosity. The increase in viscosity causes inconsistent mill lubrication. The soaps also tend to cling to metal surfaces and, as a result, are a major problem for mills. Mill managers combat the formation of soaps by performing additive adjustments to decrease viscosity and/or full or partial emulsion dumps. Both of these scenarios are a source of downtime and expense for mill managers.
Poor lubricity is another problem often experienced in the rolling of non-ferrous metals. Poor lubricity can lead to poor quality metal and/or the inability to produce a low enough gauge.
Another source of problems is biological fouling, which is a major expense to some mills. Biocides are traditionally used to treat biological fouling, but there are safety concerns associated with the proper handling of the biocides.
Therefore, it would be highly desirable to develop a new emulsion composition which exhibits improved lubricity in the hot rolling of non-ferrous metals and which resists the formation of metal soap and biological fouling.